The goal of this research program is to gain an understanding of the enzymatic generation of singlet oxygen in the body of the resultant pathological damage that this reactive species may induce. With this fundamental knowledge, specific recommendations for anticancer agents and chemotherapeutic compounds should be possible. The role of singlet molecular oxygen (IO2) and of the superoxide anion radical (O2) in enzyme-mediated peroxidation reactions in vivo has been under investigation. We recently reported that O2 is produced by the adrenodoxin reductase system. Singlet oxygen is formed by the dismutation reaction of superoxide anion radicals. Superoxide dismutase (SOD), a metalloprotein containing 2 g-atoms of Cu and Zn each, catalyzes the dismutation reaction of O2 to give ground state molecular oxygen. It is thought that SOD may serve to protect biological systems from the deleterious effects of the highly reactive O2. We have demonstrated that various copper complexes including Cu-salicylate, Cu-acetyl salicylate, Cu-aminobenzoate, Cu-UP83, and Cu-tryptophan effectively scavenge superoxide anion radicals. Among these complexes tested, Cu-tryptophan appears to be most effective. These copper complexes have the same mode of action as superoxide dismutase in catalytically removing the oxidant (O2) from solution and thereby preventing the formation of singlet oxygen. We suggest that these compounds may be potentially useful in preventing oxidative damage by O2 and IO2 in biological systems. These studies will be extended to include other types of metal complexes. The possible application of these results in the development of anticancer agents will be pursued.